What Doesn't Happen During Rem Sleep?

Sleep is a complex and mysterious process that is essential for the human body and brain to rest and recover. During sleep, the body cycles through various stages, including rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. While both REM and non-REM sleep are crucial for overall health and well-being, there are distinct differences between the two. So, which of the following does not happen during REM sleep?

Brain activity

During REM sleep, brain activity is similar to brain activity when awake. Brain imaging studies have shown that during REM sleep, the brain is highly active, and brain waves are more variable. The brain activity during REM sleep is characterised by the activation of the pons, thalamus, limbic areas, and temporo-occipital cortices, and the deactivation of prefrontal areas.

REM sleep is important for brain development, and plays a role in memory consolidation, emotional processing, and dreaming. It stimulates the areas of the brain that help with learning and memory. During this stage, the brain repairs itself, processes emotional experiences, and transfers short-term memories into long-term memories.

During non-REM sleep, brain activity is not as high as during REM sleep. Brain imaging studies have shown that during non-REM sleep, brain activity decreases in the brainstem, thalamus, and in several cortical areas including the medial prefrontal cortex. However, brain activity during non-REM sleep is not constant and homogeneous over time. It is structured by spontaneous, transient, and recurrent neural processes.

During the deepest stage of non-REM sleep, the brain waves are at their slowest, and the body takes advantage of this deep sleep stage to repair injuries and reinforce the immune system.

Eye movement

During REM sleep, the eyes move rapidly behind closed eyelids. This is where the name "rapid eye movement" comes from. The eyes move in tandem, looping back to their starting point around seven times per minute of REM sleep.

REM sleep is the fourth of four stages of sleep. It is preceded by three stages of non-REM (NREM) sleep. The first REM cycle of the night typically occurs around 60 to 90 minutes after falling asleep. The first cycle is the shortest, lasting around 10 minutes, with each subsequent cycle getting longer, up to an hour.

REM sleep is characterised by quick eye movement, irregular breathing, elevated heart rate, and increased brain activity. The brain activity during REM sleep is similar to brain activity when awake. The brain waves are fast, low-amplitude, and desynchronised, resembling the pattern seen during wakefulness.

REM sleep is important for dreaming, memory, emotional processing, and healthy brain development. It is also when the brain repairs itself and processes emotional experiences, transferring short-term memories into long-term memories.

REM sleep usually makes up about 20-25% of total sleep time in adults, which equates to about 90-120 minutes of an 8-hour night of sleep.

Heart rate

During the REM stage of sleep, your heart rate can speed up to a rate similar to when you are awake. This is because your brain activity during REM sleep is similar to that of when you are awake. If you are dreaming, your heart rate can vary depending on the activity level of your dream. For example, if you are running in your dream, your heart rate will increase.

During non-REM sleep, your heart rate slows down. In the first stages of light sleep, your heart rate begins to slow. During deep sleep, your heart rate reaches its lowest levels.

On average, an adult's resting heart rate is between 60 and 100 beats per minute (bpm). During sleep, a person's heart rate typically slows to between 40 and 50 bpm. However, this can vary depending on factors such as age, fitness level, stress and anxiety levels, and sleep behaviours.

Monitoring your sleeping heart rate can help detect irregularities and contribute to better overall health and sleep quality. A resting heart rate that is too low (less than 50 bpm) or too high (100 bpm or higher) could be a sign of trouble and should prompt a call to your doctor.

Breathing

During REM sleep, breathing becomes irregular with sudden changes in both amplitude and frequency. This irregular breathing pattern is interrupted by central apneas, which are pauses in breathing lasting 10-30 seconds. The breathing irregularities are not random but are correlated with bursts of eye movements. Unlike other sleep stages, this breathing pattern is not regulated by chemoreceptors; instead, it is controlled by the activation of the behavioural respiratory control system influenced by REM sleep processes.

Respiratory Muscle Activity:

The respiratory muscles also exhibit distinct behaviour during REM sleep. Intercostal muscle activity, which is responsible for rib cage movement during breathing, decreases during REM sleep. This reduction is attributed to REM-related supraspinal inhibition of alpha motoneuron drive and specific depression of fusimotor function. In contrast, diaphragmatic activity increases during this stage. While paradoxical thoracoabdominal movements are not observed, the thoracic and abdominal displacements are not perfectly synchronised.

Upper Airway Function:

The upper airway resistance is typically expected to be highest during REM sleep due to atonia, or loss of muscle tone, of the pharyngeal dilator muscles and partial airway collapse. However, some studies have reported no change or only a slight increase in airway resistance during this stage.

Arterial Blood Gases:

Hypoxemia, or low oxygen levels in the blood, occurs during REM sleep due to hypoventilation, or inadequate ventilation. These changes in arterial blood gases are equal to or more significant than those observed during non-REM (NREM) sleep.

Pulmonary Arterial Pressure:

The pulmonary arterial pressure, which is the pressure in the arteries carrying blood from the heart to the lungs, fluctuates in sync with respiration and tends to rise during REM sleep.

Impact of Altitude:

The link between breathing and sleep is well-established at lower altitudes. However, at higher altitudes, disruptions in sleep are often associated with changes in respiratory rhythm. Studies have shown that individuals at higher altitudes experience more frequent arousals and reduced deep sleep, resulting in poorer sleep quality.

Sleep-Disordered Breathing:

Abnormal breathing patterns during sleep can be indicative of sleep-disordered breathing or sleep-related breathing disorders. One such condition is obstructive sleep apnea, characterised by pauses in breathing due to obstruction of air passages or inadequate respiratory muscle activity. Snoring is another condition that can arise from airway obstruction during sleep.

In summary, breathing during REM sleep is characterised by irregular patterns, fluctuations in pulmonary arterial pressure, changes in arterial blood gases, and increased upper airway resistance. These changes are influenced by biological processes that affect the respiratory and muscular systems, ultimately shaping the unique breathing patterns observed during REM sleep.

Muscle tone

During REM sleep, the body experiences a temporary loss of muscle tone, also known as muscle atonia or paralysis. This is considered a normal function of REM sleep, and it is thought to be a protective measure to prevent sleepers from acting out their dreams and injuring themselves. However, in REM sleep behaviour disorder, the body does not experience this reduction in muscle tone, allowing the sleeper to move and act out their dreams. This can result in minor movements such as leg twitches, but can also lead to complex behaviours that may cause serious injury to the individual or their bed partner.

The loss of muscle tone during REM sleep is caused by the inactivation of somatic motoneurons, which are responsible for muscle movement. This inactivation is mediated by GABAB and GABAA/glycine neurotransmitters. The ventromedial medulla, which is activated by descending glutamatergic projections from the sublaterodorsal nucleus, also plays a role in inducing muscle atonia during REM sleep.

The amount of muscle tone present during REM sleep can vary depending on the species. For example, owls do not experience rapid eye movements during REM sleep since their eyes cannot move within their skulls. Some birds only lose muscle tone in certain areas, such as the neck, allowing them to keep their balance while standing on one foot.

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